Development of an application for calculating the measurement uncertainty of measurement methods for particulate, gaseous and vaporous hazardous substances

Status:

completed 12/2022

Aims:

For the measurement procedures used to determine the concentration of hazardous substances at workplaces, many components contribute to measurement uncertainty within the overall measurement procedure. This relates to both the sampling process and also the subsequent processing steps ultimately leading to the determination of a measured value. Measurement procedures are validated according to processes described in ISO standards. The validation results can be analysed with regard to the contributors to measurement uncertainty. The aim of this project is to determine the expanded range of measurement uncertainty for the relevant measurement procedure. Transferring the theoretical provisions of the standards and directives to measurement procedures used in the field can often be problematic. This is particularly true when, according to the basic requirements, the measurement uncertainty is to be calculated over the overall measurement process.

The basic requirements for the permissible level of measurement uncertainty are prescribed by DIN EN ISO 20581 and The Technical Rules for Hazardous Substances (TRGS) 402. Further provisions are contained in the standards EN ISO 22065 (gases/vapours) and EN ISO 21832 (metals/metalloids). In addition to these standards, the ISO/IEC guide "Uncertainty of measurement - Part 3: Guide to the expression of uncertainty in measurement" (GUM:1995) (which is also referenced in ISO 22065 and ISO 21832) and the EuraChem guide "Quantifying uncertainty in analytical measurement" – which is based on the ISO guide and adapted for chemical analyses – describe ways in which measurement uncertainty can be calculated.

The main objective of this project is to develop a user-friendly software tool that takes away the need for users to perform individual calculation of measurement uncertainty, and in doing so, provides for a uniform approach. The software tool will be routinely used in the context of validating measurement procedures in order to calculate the measurement uncertainty of measurement procedures for various hazardous substances classes (e.g. gases/vapours; metals/particulate matter) and will make a determination regarding the suitability of a measurement procedure.

Activities/Methods:

The first step involved selecting the parameters that are to be considered as uncertainty components for the relevant hazardous substance measurement process. This includes components of sampling and sample preparation, as well as analysis methods, which are described in corresponding models according to the specifications of the applicable standards. During the second step, the expanded measurement uncertainty of the overall measurement method was calculated using the models produced and the GUM.

A range of different cases for sampling (gases/vapours and metals/particulate matter), analysis methods (e.g. GC, HPLC, ICP-MS) and methods for producing validation samples (e.g. validation via test gases for gases and vapours, manual doping of samples for metals) had to be taken into account. A user-friendly software tool with a user interface was programmed. This software tool makes it possible to calculate the measurement uncertainty for standardised procedures and fulfils all of the requirements set out in the standards and in the GUM.

In the final step, training on how to use the software tool will be provided internally so that users within the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) can use the software tool. In addition, the software tool is also set to be made available on the Intranet (Q.wiki) and to external users via the internet (on the IFA homepage). After completion of the project, more users (e.g. in the measurement system for exposure assessment of the German Social Accident Insurance Institutions - MGU) can also be trained on how to use the software tool and on the basic features of the software tool in presentations and workshops.

Results:

Considering the GUM, mathematical models were produced and used to calculate the measurement uncertainty of the overall measurement method. The models selected were validated with software used to calculate the expanded measurement uncertainty (Qualisyst GmbH, QMSys GUM Professional). Furthermore, a successful check was carried out with an Excel-based calculation of the expanded uncertainty, which was based on the established mathematical models mentioned above. The software tool was then given a user-friendly user interface and now enables calculation of the measurement uncertainty for standardised measurement methods while ensuring that all the specifications set out in standards regarding the requirements for measurement procedures and all specifications of the GUM are taken into account.

The software tool was presented to international experts in a workshop at Airmon 2022 symposium and met with positive response. An IFA-internal presentation of the software tool has already taken place. The software tool is currently being tested with regard to practicality and applicability by a selected group of internal users as part of the method validation procedure.

The public release of the software tool and a user guide on the IFA homepage are in the pipeline. After completion of the project, training on how to use the program is to be offered for interested members of the MGU. Further national/international presentations and workshops and national/international releases are planned. There is a plan to continue to gradually develop the software and to implement additional measurement procedures with corresponding uncertainty parameters.

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